The present invention relates to a hydraulic fluid tank arrangement. The invention also relates to a method for removing gas from hydraulic fluid contained in a hydraulic fluid tank arrangement. The invention is applicable on vehicles, in particularly working machines such as e.g. wheel loaders, articulated haulers, dump trucks, etc. Although the invention will mainly be described in relation to a working machine, it is also applicable for other vehicles utilizing a hydraulic fluid tank for supplying and receiving hydraulic fluid from/to different components of the vehicle.
In the field of heavy vehicles, working machines in the form of wheel loaders, articulated haulers, dump trucks, etc. are frequently used at construction sites or the like. These working machines often comprise hydraulically operated arrangements, such as e.g. hydraulic cylinders, to control the operation of equipment associated with the working machine. For example, a wheel loader comprises a bucket which is controlled by means of at least one hydraulic lifting cylinder and at least one hydraulic tilting cylinder. The hydraulic cylinders are connected to a hydraulic fluid tank arrangement which delivers hydraulic fluid to the hydraulic cylinders and which receives hydraulic fluid from the hydraulic cylinders. Hence, a closed loop is provided where the hydraulic fluid is directed from the hydraulic fluid tank arrangement to a hydraulic cylinder, and thereafter back to the hydraulic fluid tank arrangement by means of a return line.
When the hydraulic fluid is provided to the hydraulic fluid tank arrangement via the return line, it often comprises a substantial amount of gas bubbles. The gas bubbles are generated during the operation of the hydraulic cylinder and are thus provided into the hydraulic fluid tank arrangement. The gas bubbles are unfavorable for the operation of the hydraulic cylinders since they may cause cavitation damages in the hydraulic fluid system. Also, the overall capacity utilization of the cylinders may be reduced if gas bubbles are present in the system. Further, the control of operation of the hydraulic cylinders may be reduced by means of uncontrolled disturbances that arise due to the gas bubbles.
Prior art solutions describe various ways of removing gas bubbles from the hydraulic fluid in a fluid tank. For example, a solution to the problem has been to introduce a deaeration device in the hydraulic fluid tank that removes the gas bubbles from the hydraulic fluid before the hydraulic fluid is evacuated from the tank and directed to e.g. the hydraulic cylinders of the working machine.
However, although prior art describes a way of removing gas bubbles from hydraulic fluid in a fluid tank, further improvement is still needed, such as, for example, to further increase the reliability of sufficiently removing the gas bubbles from the hydraulic fluid.
It is desirable to provide a hydraulic fluid tank arrangement which improves the removal of gas from hydraulic fluid compared to the prior art solutions.
According to a first aspect of the present invention, there is provided a hydraulic fluid tank arrangement for a working machine, the arrangement comprising a hydraulic fluid tank; an inlet portion for receiving hydraulic fluid into the hydraulic fluid tank; and an oil filter arranged in fluid communication with the inlet portion; wherein the hydraulic fluid tank arrangement further comprises a gas removal device arranged in fluid communication with the oil filter downstream the inlet portion and upstream the oil filter for removing gas from the hydraulic fluid before the hydraulic fluid reaches the oil filter.
The inlet portion of the hydraulic fluid tank arrangement should in the following and throughout the entire description be interpreted as the inlet of the tank arrangement where hydraulic fluid that has circulated through the hydraulic circuit enters. For example, the hydraulic circuit may comprise the hydraulic cylinders of the working machine.
Furthermore, it should be understood that the gas removal device is arranged in direct downstream fluid communication with the inlet portion. Thus, no oil filter is present between the inlet portion and the gas removal device. In detail, the gas removal device is in filter-free downstream fluid communication with the inlet portion of the hydraulic fluid tank arrangement. Still further, the gas removal device may be any suitable arrangement that removes gas from hydraulic fluid. As an example of a gas removal device, a cyclone deaerator will be described below.
The oil filter should be understood as a filter which is used for removing contaminants from the hydraulic fluid. Thus, after the hydraulic fluid has passed the gas removal device, contaminants, i.e. micro particles, are removed from the hydraulic fluid by means of the oil filter.
The present invention is based on the insight that by providing a gas removal device upstream the oil filter, the gas bubbles contained in the hydraulic fluid will be removed from the hydraulic fluid before the hydraulic fluid reaches the oil filter. Advantages of removing gas bubbles from the hydraulic fluid before the hydraulic fluid reaches the oil filter is that it is easier to separate the relatively large bubbles that enters the hydraulic fluid tank arrangement, in comparison to arranging the gas removal device in downstream fluid communication with the oil filter which will result in relatively large gas bubbles being divided by the filter into smaller gas bubbles which are more difficult to separate from the hydraulic fluid when entering the gas removal device. Hence, when gas bubbles are directed through a filter they will be divided into smaller gas bubbles. Also, the relatively large gas bubbles separated from the hydraulic fluid by means of the gas removal device will rise towards the surface of the hydraulic fluid in the hydraulic fluid tank in a more rapid manner compared to smaller gas bubbles. An effect of having an increased upward directing speed of the bubbles, i.e. such that the gas bubbles reach the hydraulic fluid surface more rapidly, is that the risk of getting bubbles into e.g. a pump provided in connection to an outlet of the hydraulic fluid tank arrangement is reduced. For example, if the hydraulic fluid velocity down to the pump is higher than the upward directing velocity of the rising gas bubbles, the gas bubbles will be sucked down to the pump. This is hence at least partly alleviated by separating larger gas bubbles which will have an increased upward directing velocity in comparison to smaller gas bubbles. Still further, larger gas bubbles have an increased tendency to crack when they reach the hydraulic fluid surface in comparison to smaller gas bubbles. Hereby, a total reduction of gas bubbles will be provided in the hydraulic fluid tank arrangement.
Still further, in a working machine there is often a relatively large amount of differential flow in the tank, which means that the flow out from the hydraulic fluid tank arrangement is relatively large in comparison to the flow into the hydraulic fluid tank arrangement, or vice versa that the flow into the hydraulic fluid tank arrangement is relatively large in comparison to the flow out from the hydraulic fluid tank arrangement. By providing the gas removal device in direct fluid communication downstream the inlet portion of the hydraulic fluid tank arrangement, and in upstream fluid communication with the oil filter, will provide approximately the same hydraulic fluid flow into the gas removal device as is directed out from the gas removal device. In detail, when using a pump to provide hydraulic fluid to the cylinders, there will be a differential flow in the tank which means that the flow of hydraulic fluid out from the tank is larger than the flow into the tank. By providing the gas removal device according to the invention separates the gas removal device from the pump which makes it a suitable environment for the gas removal device since the differential flow will be relatively low. Having a gas removal device in connection with the pump, according to prior art solutions, will on the other hand result in that hydraulic fluid is also taken from the tank to sufficiently supply fluid to the pump, and thus bypassing the gas removal device providing a relatively large differential flow which is not satisfactory.
According to an example embodiment, the hydraulic fluid tank arrangement may further comprise an outlet portion for providing hydraulic fluid out from the hydraulic fluid tank.
The outlet portion of the hydraulic fluid tank arrangement should in the following and throughout the entire description be interpreted as an outlet where hydraulic fluid is evacuated from the hydraulic fluid tank arrangement to e.g. hydraulic cylinders of the working machine.
According to an example embodiment, the hydraulic fluid tank may comprise a first hydraulic fluid chamber, the gas removal device being arranged in fluid communication with the first hydraulic fluid chamber for providing gas removed from the hydraulic fluid into the first hydraulic fluid chamber.
An advantage is that the gas removed from the hydraulic fluid is provided into a well defined space, which reduces the risk of providing the removed gas into the outlet portion of the fluid tank arrangement.
According to an example embodiment, the hydraulic fluid tank may comprise a second hydraulic fluid chamber, the second hydraulic fluid chamber being arranged downstream the oil filter in fluid communication with the oil filter and the outlet portion of the hydraulic fluid tank arrangement.
Hereby, the hydraulic fluid entering the oil filter downstream the gas removal device will be provided into the second chamber. Thus, the second chamber will be provided with hydraulic fluid which is substantially free from gas bubbles. An advantage is thus that the gas removed from the hydraulic fluid is provided into the first hydraulic fluid chamber and the hydraulic fluid which is substantially free from gas bubbles is provided into the second hydraulic fluid chamber. Hereby, the relatively clean and gas free hydraulic fluid provided in the second hydraulic fluid chamber can be used for further operation of e.g. the hydraulic cylinders of the working machine.
According to an example embodiment, the first hydraulic fluid chamber may be in fluid communication with the second hydraulic fluid chamber. An advantage is that the hydraulic fluid in the first hydraulic fluid chamber may also be used for further operation of e.g. the hydraulic cylinders of the working machine. The first and the second hydraulic fluid chambers may be separated by means of a separation wall as will be described further below, or the first and the second hydraulic fluid chambers may be arranged as separate fluid tanks or reservoirs which are interconnected to each other by means of a hose or tube, or the like.
According to an example embodiment, the hydraulic fluid tank arrangement may further comprise a venting filter arranged in communication with the first hydraulic fluid chamber for directing gas in the first hydraulic fluid chamber out from the hydraulic fluid tank arrangement.
Hereby, gas which is present in the first hydraulic fluid chamber above the surface of the hydraulic fluid therein can efficiently be directed out from the hydraulic fluid tank arrangement via the venting filter. The venting filter may itself have filter properties which prevent contamination to be expelled from the hydraulic fluid tank arrangement to the surrounding environment of the hydraulic fluid tank arrangement.
According to an example embodiment, the gas removal device may comprise a gas outlet portion for evacuating the gas removed from the hydraulic fluid out from the gas removal device.
The hydraulic fluid entering the gas removal device may, due to a slight overpressure in the gas removal device, be forced towards the same outlet as the gas bubbles. In order to enable that the majority of the hydraulic fluid is directed towards the oil filter while the removed gas is directed through the gas outlet portion, a gas outlet portion is provided. The gas outlet portion should thus be interpreted as a portion of the gas removal device in which the gas exits the gas removal device. The gas outlet portion may, according to an example, be formed as an orifice which forces the main part of the hydraulic fluid entering the gas removal device to be directed towards the oil filter.
According to an example embodiment, the hydraulic fluid tank arrangement may further comprise a separation wall dividing the hydraulic fluid tank into the first hydraulic fluid chamber and the second hydraulic fluid chamber, the separation wall extending from an upper wall of the hydraulic fluid tank to a level below the gas outlet portion.
Hereby, a clear separation of the first and second fluid chambers is provided. An advantage of arranging the separation wall to extend to a level below the gas outlet portion is that it is further secured that the removed gas is directed into the first hydraulic fluid chamber. Hence, the separation wall further reduces the risk of providing gas bubbles into the second hydraulic fluid chamber. Moreover, providing the gas bubbles into the first hydraulic fluid chamber which is separated from the second hydraulic fluid chamber provides an environment for the gas bubbles which is not affected by the suction of hydraulic fluid out from the second hydraulic fluid chamber. Hence, the gas bubbles will be able to rise toward the surface of the first hydraulic fluid chamber where they will be able to crack. The separation wall may extend vertically from the upper wall of the hydraulic fluid tank. However, the present invention should not be construed as limited to a vertical extension having a 90-degrees angle from the upper wall, the separation wall may have an inclination of more/less then 90 degrees in relation to the upper wall, such that a horizontal component of the separation wall is present as well.
According to an example embodiment, the separation wall may further comprise an opening for directing gas in the second hydraulic fluid chamber into the first hydraulic fluid chamber.
Gas present in the second hydraulic fluid chamber may thus be directed into the first hydraulic fluid chamber and thereafter further through the venting filter. A gas passage is thus provided between the first and the second hydraulic fluid chambers.
According to an example embodiment, the hydraulic fluid tank arrangement may comprise a pump arranged in fluid communication with the outlet portion downstream the outlet portion.
Hereby, hydraulic fluid is allowed to be pumped to the various hydraulically controlled components of the working machine. The pump may be a hydraulic pump.
According to an example embodiment, the gas removal device may be a cyclone deaerator.
Hereby, a relatively simple and cheap gas removal device may be provided. A cyclone deaerator is also advantageous since it can be made relatively small in size while still being robust and functional.
According to a second aspect of the present invention, there is provided a working machine comprising a hydraulic fluid tank arrangement according to any one of the above described embodiments in relation to the first aspect of the present invention.
According to a third aspect of the present invention, there is provided a method for removing gas from hydraulic fluid contained in a hydraulic fluid tank arrangement comprising a hydraulic fluid tank, wherein the method comprises the steps of providing hydraulic fluid to an inlet portion of the hydraulic fluid tank arrangement; directing the hydraulic fluid through a gas removal device arranged in downstream fluid communication with the inlet portion for removing gas from the hydraulic fluid; and directing the hydraulic fluid to an oil filter arranged in downstream fluid communication with the gas removal device.
According to an embodiment, the hydraulic fluid tank may comprise a first hydraulic fluid chamber, the gas removal device being arranged in fluid communication with the first hydraulic fluid chamber, wherein the method may further comprise the step of providing the gas removed from the hydraulic fluid into the first hydraulic fluid chamber.
Further effects and features of the second and third aspects of the present invention are similar to those described above in relation to the first aspect of the present invention.
Further features of, and advantages with, the present invention will become apparent when studying the appended claims and the following description. The skilled person realize that different features of the present invention may be combined to create embodiments other than those described in the following, without departing from the scope of the present invention.